It is known that the wet combustion of organic materials in water will produce high pressure, heated water with enough internal energy to justify the recovery of mechanical energy. One such method of recovery includes the separation of steam from the other fluids of the mixture, utilizing an expansion turbine to produce the energy. However, the separation of steam from the fluids mix results in most of the actual energy being left in the high pressure and temperature water, and therefore not available for energy recovery. At room pressures, less than seventeen percent of the heat energy is in the fluid, and the rest is in the steam. At 2000 pounds per square inch pressure, sixty percent of the heat energy is in the water and the rest is in the steam. If the steam is separated at two thousand pounds pressure, most of the heat stays with the water, and is denied to the energy recovery from steam.
It has been found that the higher the pressure, the poorer the efficiency of separation. At 3200 pounds pressure, such as disclosed in U.S. Pat. No. 4,543,190, virtually all of the energy is in the water, because at supercritical conditions, by definition, there is no phase difference between steam and water. The problem this creates is that for every gallon of water used for power recovery, another gallon of water has to be raised to the operating pressure, and very little net energy, if any, is recovered for use outside of the system.
The problem is further complicated in that a hundred pounds of steam only yields the equivalent of ten to twenty pounds of steam in the form of electrical energy. This is due to the inherent inefficiency in the expansion turbine wherein the majority of the energy is lost when the spent steam is condensed and that heat of condensation is lost to the cooling tower.
Most energy recovery methods heretofore known in the art have consisted primarily of the type employing recirculation of hot water. There exists a need to recover the internal energy from a mixture of high pressure and high temperature water with the gases of combustion, all in the heterogeneous mixture typical of the wet oxidation process.